TRANSACTIONS OF SECTION C. 553 
of the foliation of the crystalline schists of sedimentary origin must be attributed 
to earth movements and associated with the phenomena of slaty cleavage. 
The Rey. Osmonp FisHEeR made the following communication :— 
L used to think that the corrugations of the earth’s crust were due to compres- 
sion through the shrinking of the interior. To judge of the sufficiency of this cause 
the first thing to be done is to seek a measure of the compression, and then to 
compare the result of the effects of cooling with the actual amount of compression. 
The most satisfactory measure appears to be the thickness of the layer which 
the corrugations would form if levelled down. The question then becomes a 
question of how much. In 1863 Lord Kelvin (then Sir W. Thomson) formulated 
a law of secular cooling upon the hypothesis that the interior is solid. Adopting 
a probable value for the contraction of rocks in cooling, I calculated the thickness 
of the layer which would be produced by the corrugations resulting, and found it 
far short of that which the existing inequalities would form if levelled down. 
Mr. Mellard Reade and Dr. Davison subsequently discovered the existence of a 
level of no strain within the crust, and this greatly reduces the possible amount 
of corrugations. The conclusion at which I arrived was that, on the hypothesis 
of a solid globe, secular contraction through cooling would not account for the 
corrugations. : 
Numerous phenomena suggest to the vulcanologist that the substratum is a 
liquid magma holding water-gas in solution. The free yielding of the substratum 
is also testified by the phenomena of isostacy. I have therefore endeavoured to 
estimate the amount of corrugations which would be produced by a cooling globe 
also on this hypothesis. But although they would be slightly greater than in the 
case of a solid globe, they still fall far short of those actually existing. I there- 
fore argue that the corrugations of the crust are not due to the shrinking of the 
peer away from the cooled crust, whether we regard the interior as solid or 
iquid. 
My own view of this vexed question, which is based on the considerations 
given below, is that the substratum is affected by convection currents, and that 
these ascend beneath the oceans, and flowing horizontally towards and beneath 
the continents, and descending beneath mountain chains, are the cause of the 
compression of the crust, and other disturbances, of which we are in search. 
It is, in the first. place, necessary to combat the dictum of leading physicists 
that the interior of the earth is solid. It has been asserted that unless the earth 
is extremely rigid bodily tides would be produced, and that there would be no rise 
and fall of the water relatively to the land. Ifthe earth was a smooth spheroid, 
covered with a uniformly deep ocean, this would, no doubt, be true; but as matters 
stand the tides of short period are affected by local irregularities, known as the 
establishment of the port. If the substratum of the crust is liquid, isostacy 
requires large protuberances of its underside, which would cause irregularities in 
the tides in the magma analogous to those in the ocean; and unless these agree 
in time, in height, and in place with the water tides, the latter will not be 
obscured by them, and may even be augmented. | 
Of tides of long period the fortnightly is the most important, but I think I 
have shown in the Appendix to my ‘ Physics of the Earth’s Crust’ that it had not 
been proved by fifteen years of observation that any such tide existed,! which 
would be an argument in favour of the liquidity of the interior. 
The peculiarities of the transmission of earthquake waves to great distances 
through the body of the earth have been appealed to as proving to all ‘except 
some geologists’ that the earth is solid.» The disturbance first arrives as a series 
of minute tremors. These have been considered to be waves of compression. 
They are soon followed by somewhat larger disturbances, which have been con- 
sidered to be waves of distortion. Since waves of distortion could not be 
propagated in a liquid, it is maintained that the earth is hereby proved to be 
solid. In reply to this argument, I have shown that if a liquid magma holds gas 
1 Page 34, Nae 2 Darwin's Tides, p. 236, 
